Feed-back system for electronic tubes comprising hollow body resonators



Jan. 18, 1949. D. H. sLoAN 2,459,593

FEED-BACK SYSTEM FOR ELECTRONIC TUBES COMPRISING HOLLOW BODY RESONATORSFiled March 1v, 1944 43 .E BY

ATTORNEY Patented Jan. 18, 1949 FEED-BACK SYSTEM FOR ELECTRONIC TUBESCOMPRISING HOLLOW BODY RESONATORS DavidH. Sloan, Pittsburgh, Pa.,assignor to`WestinghousefElectric Corporation, East Pittsburgh, Pa., .acorporation of Pennsylvania 2 Claims. t 1

This invention relates `to a `feed-baci: :system for electronic tubesand has particular relation to `a `fee`d=back system `for `use with 'atube of the resnatron type iorgenerating ultra high frequency power.

A 'tube of the resnatron `type generally com prises a pair of resonatorsadapted to lhave relectromagnetic oscillations of substantiallyxthe samefrequency.` established therein. A .cathode is mounted within `the firstresonator and an .anode is'mounted within the second resonator. The two`resonators are positioned'adjacentr'each other and have openings in`the adjacent walls thereof to permit a flow oi electronsufromV thecathode to the anode. One or more grids are located between the cathodeandanode and preferably include a control grid formedby 'the .wall ofAvthe irst `resonator about `the openings therein :and anacceleratinggrid formed by the Wall of the second resonator about the Openingstherein. Means are then provided to supply current through `the cathodeto'heat it and to impressa direct-current potential differencebetweenthe anode and cathode, the accelerating grid and cathode, and thecontrol grid and cathode.

The resnatron `tube operates `as a tuned-plate, tuned-grid, class Coscillator with the rstiresonator in the controlrgrid-cathode circuitandithe second resonator in the anode or plate circuit. Each ofthe tworesonators isrdesgnedto have a principal mode of oscillation in "which.the `vector of the electric field is substantially parallel to theelectron path betweenthe cathode andfanode and the fields within theresonators :have a-delnite phase relationship. During operation theanodeand acceleratingogrid have a `relatively high, positive directcurrent voltage thereon frelative to the cathode tending to liberateelectrons from the cathode but the control gridhas 'afnegative voltagesuch that a group of electrons "are liberated from the cathode onlyduring the peak portion of each `half cycle of the iield in the iirstresonator in which that field `tends 'to Vaid in effecting `liberationof `electrons and movement thereof toward the anode. Thus sharp pulsesof electrons are liberated at regular intervals from the cathode.

After liberation, `the electrons are `accelerated in their movementtoward the anode by l'the high voltage on the accelerating grid.Thespa/c'ingbetween the *cathode `and anode with respect to the speed ofthe 'electrons provides #an electron transit time of one-half cycle.Thus, the zliberated electrons rst receive lenergy uirom #theroscil-Llating `field of the rst resonator aswelinsrom l the -.di1ec.t currentvoltage iields but .they .enter the field of .the :second :resonatorwhile .it op poses their motion and the electronsreonsequentl;rgiveupenergy-to the eldpf the second resonator' to iproduce fthe desired`oscillations therein.

A portion rof ithe @power thus :generated in .the second :resonator is`:fed-back to :the .rst `resonator .to maint-ain the ldesiredoscillations rtherein. This ifeedback is accomplished through aconcentric transmission gline having one .end coupled -to :the :secondresonator by ra coupling loop 1.0i :the .usual construction and vtheother end coupled into :the-first :resonator by another similarcoupling.loop. The couplingrproduoesoscillationsin .the :first resonator rinwhich the controlggrid '.toocathode high frequency voltage is inphasewith rthelanode toqaccelerating grid high frequency voltage. The.remaining fpower .is extraoted :fromdshe second resonator by stillKanother coupling loop connected to an outputrtransmission dine. l

The resnatrontube, rwhenproperly constructed, operates asdescribed.`rHowlever, `it has been hfound desirable eto improve -the :feed-back`coupling fsystem .and 4to increase the .powerfoutput :available from .al.tube of ithis type. The energy -.delivered by thefrelectrons :to :the.eld -o'f .the .second resonatmnnay :be increased by increasing thevoltages @impressed .on 1the various .elements which increases Ain =turnthespeed of lthe electrons .fentering .the `second resonator. With :the.increased speed,` however.the transit time of the electrons is`reduced. Whenstlietransit .timerof the elecf trans fis reduced, anincrease lin `the `spacings between rthe 1 elements along the lelectronpath `is rrequired which @in .turnirequires a `'higher 'voltage tomaintain .therelectronspeedso kthat.et-:satisfactorytpower :increasebyfthis Lrneans-is rimpractical.

.The feed-back -icoupling 1 system as "usedin lprior tubes :isarsourcefof ,power `.lossas :well as asource of considerable:manufacturing fdiiculty. It :is extremely difficult and .almostLimpossiblegrrom :a practical standpoint to avoid rstanding `wavesin the`:feed-back line. 'Iheserstanding `waves cause appreciable :power lossesand introduce `thigh voltage Aproblerrvs. :In reddition, `glass rsealsare usually employedxin A`theieed-b1arckiine to permit the maintenanceof vthe necessary Vhigh `vacuum fwithinrthe tubc.- However, rthefhighMoltagesresmtingpfromwthestandirrg waves :in :the 'feed-.back line, are'very `rlestructive `of the tgl-ass and, with gesfinthe A.form of air inthe line, rthe A.sealsare often Abrokensnoring operation of the ytube.

'To avoid the troubles encountered with Vthe glass seals, :avacuum-.tight feed-.back` `line has Another object of my invention is toprovide a new and improved resnatron tube .having an increased poweroutput.

A further object of my invention is to pro- V vide a novel resnatrontube having a new and improved feed-back system.

Still another object of my invention is to provide a novel resnatrontube having a highly ef'- cient feed-back system which avoids theintroduction of problems associated with maintaining a vacuum.

More specifically, it is an object of my invention to provide a new andimproved resnatron tube having a novel feed-back system and an increasedpower output.

-Myinvention arises from the realization that the direct-currentvoltages employed with the resnatron tube can be increased to increasethe electron voltage, and, therefore, the power output, with the samespacings between cathode, grids andanode if the phase of the .voltagecomponent of the field within the first resonator be- 4tween the controlgrid and cathode is shifted to lag by an amount of the order of 90degrees behind 'the voltage component of lthe eld of the secondresonator between the anode and accelerating grid. If the Voltage withinthe rst resonator lags 90 degrees behind that in the second resonatorinstead of being in phase, the electron voltage may be increased by fourtimes with the transit time of the electrons reduced to onequartercycle.

In accordance with my invention, a 90 phase shift of the field voltageof the rst resonator relative'to -the' second can be obtained byconnecting a small capacity between the anode and cathode and tuning thefirst resonator, Within which the cathode is mounted, to substantiallythe same frequency as the second resonator so thatl the'cathode tocontrol grid impedance is neither inductive nor capacitive. Thiscapacity may be conveniently obtained by positioning a conductive memberadjacent to, but spaced from, the anode, and conductively connecting thememberto the cathode. Preferably, this arrangement comprises amolybdenum or tungsten wire attachedto the cathode and extending throughthe grids into the anode region with the end portion of the wire bent atright angles to form a conductive member adjacent to, but spaced from,the anode. In some eases, where not as much capacity is required, thewire need not be bent at the endneXt the anode but instead may merelyextend toward the anode with the end of the wire spaced therefrom.

The coupling wire may be attached to any part of the cathode other thana point of zero voltage with respect to the' control grid, but ispreferably connected at a region of maximum voltage. At

this region on the cathode, the anti-resonant impedance of thecathode-grid circuit is at its largest value, with the grid-cathodevoltage at a maximum and the current at a minimum. Such an anti-resonantimpedance acts as a resistance connected in series with the `capacitanceexisting between the wire and the anode. When the eld in the secondresonator is in a direction that the 4 anode is positive, current owsfrom the anode through the capacitance, wire and resistance. The voltageestablished across the resistance by the current leads the highfrequency anode-accelerating grid voltage by about degrees with thecathode. positive relative to the control grid. Consequently, the eld inthe rst resonator reaches a maximum in a direction aiding movement ofelectrons from the cathode to the anode electrons leaving the cathodeduring the peak vportion of a half-cycle of the rst resonator eld inwhich that eld is in a direction aiding movementof the electrons, enterthe second resonator when the eld thereof is in a direction opposing theelectron motion and the electrons give up energy to the eld of thesecond resonator.

If the first resonator is tuned to a slightly different resonan-tfrequency, the amount of phase shift is changed as may be necessary ordesirable with different spacings and different direct-current voltages.

The novel features which I consider characteristic of my invention areset forth with more particularity in the accompanying claims. Theinvention itself, however, with respect to the construction andoperation of an embodiment thereof, as well as further objects andadvantages ofthe invention, may be best understood from the followingdescription of a specific embodiment with reference to the drawing, inwhich:

. Figure 1 is a cross-sectional View of a resnatron tube embodying myinvention;

Fig. 2 is an enlarged, partial view of a crosssection of the tube shownin Fig. 1, as taken along line II--II;

Fig. 3 is an enlarged, partial view of a crosssection of the tube ofFig. 1 as takenalong the axis;

Fig. 4 is an elevational view of one of the anode units; and v Fig. 5 isa top View of the anode unit shown in Fig. 4. l

As shown in Fig. 1, the main portion-of the resnatron tube is enclosedwithin a generally cylindrical; chamber comprising an upper, cir-l cularplate unit II, two coaxial, cylindrical, metallic members I3 and I5 ofthe same diameter spaced apartby a coaxial, glass cylinder I1 of thesame ldiameter sealed therebetween, with the upper cylindrical member I3secured to the upper plate unit Il and the lower cylindrical member I5secured to an intermediate plate unit I9. Another cylindrical member 2Iis secured to the bottom of the intermediate plate unit I9 and the lowerend of member 2l is secured to a bottom plate 23. A cathode unit 25extends through a central opening in the bottom plate 23, being securedtherein by a cap member 21 and support 28. A cooling fluid, supplychamber body 3U is threadedly mounted in a central opening in theupperplate unit II. The entire chamber 'I is sealed and a vacuum iscreated and maintained therein by a Ivacuum pump connected to theinterior of the chamber by a passage which does not appear in Fig. 1.

The cathode unit 25 includes a plurality of cathode filament wires 29spaced from each other but arranged to form a generally cylindricalcagelike structure in the center and about the axis of, the. .chamber 1,and a plurality of concentric 8 tubular membersl as `s'lrrown iin Fig 3.Complete details-ofthe cathode unit 525` are disclosedinmy copendingapplication, Serial No. 526,883, 'led March 17,11'944and now U."S.\Patent No. 21,451,- 981,granted October 119, 19118.

The upper ends `oftlie lamentwires `29 `are soldered aboutthe`circumference rof a 'threaded nut '53| whichis mounted ontheupper fendof one ofthe 'tubular members 33 of `the cathode unit 25. Fromthefnutl,each filament `Wire Z9 extends lradially Ioutward a short 'distance andthen downwardly, parallel to theaxis,` with 'the lower "endl ofthelament wire extending'radially inward-towardthe axis and secured -toanother tubular member 35-Within thecathodeunit. The twotbularmembersand '35jto `which:thefilament wires "29'are attached are spaced fromeach other Lby insulating `pellets 31. A"'I'he central tubularl memberlit!! ofthe cathode unit *25extends upwardly beyond the filament wires29 to a tuning vplate 45. jThe ltubularmember' 39 is `movable verticallyto move the'tuning `'plate 45, by rotation ofthehand `wheel 43 jat thebottom of the resnatrontube. The tuning plate 45i`s 'connected to thetubular member "33 through a ilexible bellows 41. 1

VA cylindricalmember 49 of conductive material is also positionedcoaxially within thechamber 1 andsurrounds the cathode unit 25. Thismember `49, hereinafter called the control grid member, is mounted onanother horizontal plate supported from bottom `plate 23 by a pluralityof insulators 52. An end plate 53, spaced from the tuning plate 45,extends lacross the upper end of the control grid member. The lowerendof the control grid member 49 is spaced from the cathode unit 25 butis associated with still another tubular `member 55, mounted on thesupport `28 for the cathode unit 25, to form a choke `for highfrequencyoscillations. With this structure, a flrstresonator is formed by theplate 53, the control grid member49, member 55, and the cathode unit 25,the `cathode lament wires 29'being positioned within this firstresonator.` A cooling UicLsuch-as water, is supplied through an `inletpipe 561and plate-5I to cool the controlgrid member 49, `in a mannerfully disclosed in my aforesaid copending application, and passesvoutoutlet pipe 58. i i l i.

Openings 51 are provided inthe wall of the control :grid :member V49opposite each ,of ,thexilamentv wires 29, as illustratedin Fig. `2 to`provide aJg'rid. Means are also provided to cool the control gridmember 49 but they are not visible Ain thecross-sectionoflig. 1 but areillustrated in my aforementioned copending application.

A cylindrical unit `63, designated the accelerating grid unit,`comprises :a plurality of 'vertical pipes 65 of conductive materialarranged to outline la cylinder concentric with, and surrounding, thecontrol grid member '49. The pipes 65 are spaced `fromeach other,as`shown in `Fig..2, so thatfin the vregion of the `filament Wires 29, thespaces between adjacent lpipes are radiallyoppo site correspondingfilamentwires 29and .openings 51 inthe control grid member, `.wherebythepipes 95 form a grid. Secured to and surrounding the pipes 155 abovethe region of the Afilament wires is a conductive `metal `cylinder 61. Asimilar cylinder 68 -surrounds the pipes E5 `below `the region of ythefilament wires. A cap6`9 `is secured across the top of the cylinder61and has openings extend, the capi-having r-anfiliterual `passage-inccmmimicationwith:the open endsrof all of pipes 65. l

The entire accelerating gridrunit 63 -ismounted on a horizontal 'plate10 `which `is-supported lfrom l the bottomlplate 123 'by a plurality ofiinsulators (not shown). A cooling Aiiuid, `such as `water, fis suppliedthroughian `inlet `-pipe (notshown) and an `internal passage *1I inplate 10 to one-half of pipes diii. "Thefluidflows up'these pipesto cap69 and returns through the other half -o'f the pipes to "anotherinternal passage 13 .in plate '1B connected lto an outlet pipe(nots'hown).

The bottomoi the cooling `fluid-chamber body 30 within thechamber 1 lhasa plate 89 'secured thereon ywhich isfspaced from the cap S9 'ontheacceleratingngrid `member 63. This plate -89 is circular and supports acylindrical member i91 which in turn supports theanode structure.Another cylindrical member 93 foi slightly larger diameter `than theanode supporting member 9| is mounted onthe lower plate 10 and extendsupward with its upper end surrounding the anode supporting memberandcooperating'therewith to form a quarter 'wave "length, high frequencychoke. These two members 9| and 93 `with the plate89, lowerplate finlandthe accelerating grid member "B3 with Yits cap 69 form a secondresonator.

The anode ofthe resnatron tube comprises a plurality of anode units 15,as shown in Figs. l, 4 and'5`, arranged within the second .resonator ina circle around the accelerating grid. .Each of the anode units '15comprises afconvoluted section of `a hollow pipe `11 of `highlyconductive material, such as copper, through which a cooling uid, suchas Water, is to be passed. The two ends "19 and 'di of the hollow` pipeextend upwardly -frorn the convolutions with one endlH connected toacoolinguid .chamber S2 in body 3l)` `supplied with cooling fluid froman inlet .pipe line 85and with the .other end Bl connected to anotherchamber `83in body 35i Afrom which duid isremovedthroughan .outletline.81.

'Ifhe convolutions .of each .anode unitincludes apluralityofsubstantially parallel and coextensive vertical, pipe portions whichareslightly longerthan the slotsin `the acceleratingandcontroljgrids 1and,of coursaareparallel `to the verticallament wiresZS. When all .of theplurality ofanode .units arearranged adjacent each other inlacircleabout the 4accelerating grid as shown in Fig.` 2, that `part `ofthecomplete `anode. having the` largest .diameter is made .upof pairs.of adjacent, Verticalpipe portionsg in engagement .with eachotherwithleach .pair positioned radially opposite .a filament Wire 29 so that.the center line ofthe electronpathirom a iilamen't wire may berepresentedbydotted line 92. The otherconvolutions cooperate `with each,pair 9i! .to outline a groove radially opposite each filament wire intowhich the corresponding electron path projects. Further details oftheanode structure and the obi jects and` advantages thereof aredisclosedinmy copending application, Serial No. 526,883, iiled March"17,'1944.

A `plurality of feed-back coupling wires 99 are attached atome end 'tothe `cathode unit 25 in the 'rstresonator and extend radially throughthe grids`l59 and Shinto the second resonator. Preferably, fourof thesecoupling Awires are yemployed,"the number, of courseydependingupon theamount `of lfeed-back power required to operate the 'liirst resonator.`As shown 'in Figs. i2 and '3, eachoffthe-couplingwvires 99 issecuredtothe end o atubularlmember lllfl threadedly engaged with the tubularmember 33 supporting the upper end of the iilament wires 29 and extendsradially through a set of openings in the grids for which the filamentwire is omitted. The outer end prtion of each coupling wire is bent atright angles to form a conducting member adjacent and parallel to, butspaced from,.the anode. Thus the coupling wire 99, in effect, provides acapacitance connected between the anode and cathode.

As previously mentioned, the end portion of the coupling wire need notbe bent in some cases. It is also to be noted that the omission of afilament wire for each coupling wire may be avoided by connecting thecoupling wire to the base |00 of bellows 47 and extending it radiallyabove the lament wires through slightly enlarged openings in the grids.

The two resonators are designed so that their electric field vectors arealong radial lines. Consequently, alternate points` of minimum andmaximum voltage appear along the length of the cathode unit 25. The-coupling wires 99 may be connected to the cathode unit at any pointother than a zero voltage point. However, it is preferable to connectthe coupling wires at a point of maximum voltage with respect to thecontrol grid. This is the point of minimum current and the anti-resonantimpedance of the cathode-grid circuit with the rst resonator tuned tothe same resonant frequency as the second resonator acts as a resistanceconnected in series with the capacitance existing between the couplingwire and the anode. The voltage drop across the resistance is thenshifted on the order of 90 degrees in phase relative to the highfrequency voltage be tween the anode and accelerating grid. Aspreviously explained, the voltage drop across the resistance iseffective to maintain the oscillations in the cathode resonator with theeld of the rst resonator rising to a maximum inthe direction aidingmovement of the electrons 90 degrees behind the field in the secondresonator. If the coupling wires are connected at -some point other thanthat of maximum Voltage, the impedance of the cathode-grid circuit issmaller and a greater capacity would be required to feed back the samepower. Tuning of the rst resonator to another frequency changes theeffect of the impedance and produces a different phase shift. It is tobe noted that the second resonator may also be tuned by raising orlowering plate 89 by screws 04 which may be used to bend the diaphragm96.

The cathode unit 25 also includes another concentric tubular member IOIpositioned between the members 33 and 35. The tubular member IOI isconnected at its upper end to the member 33 but is spaced from thetubular member 35 and extends downwardly for a distance equal to theone-quarter wave length. Thus a low impedance is established betweenmember 35 supporting the lower ends of the lament wires 29 and themember 33, supporting the upper ends of the filament wires and thecoupling wires, at the point A. This, in eiect, provides a shortIcircuit for high-frequency currents in the lament and coupling wiresand prevents the escape of high-frequency power through the filamentsupply circuit which is connected to tubular members 33 and 35.

Direct-current voltages are impressed on the anode, cathode and grids ofthe resnatron tube as shown schematically in Fig. 1. A source ofdirect-current potential, such as a battery |03, has its positiveterminal I05 connected to the body 30 and, therefore, to the anode. Anintermediate tap |01 on the battery |03 is connected to the plate I0supporting the accelerating grid member' 63 and thenegative terminal|09, is connected through a threaded plug III in housing yI I3 to thetubular member 33 which is connected tothe The tubular upper ends of thefilament wires. member 35 supporting the lower ends of the lament wiresis grounded through the threaded plug II5 in thesupport 28. Filamentcurrent issup-` plied from a source I I9 through a transformer IZIconnected to plugs III and II5. The control grid member 49lis connectedthrough the plate 5 I which supports it and a resistor II1 to the nega-ytive terminal |09 of the battery |03. Typical direct currentvoltageswhich have beenv used in operating a resnatron tube constructedaccording to Fig. 1 with a 90 degree phase displacement. in the elds,establish the anode at 10,000 volts.

and the accelerating grid at 7,000vo1tsf The conf` trol grid isoriginally at zero voltage but when the oscillations are initiated,current flows from the control grid to the cathode and the resultingpotential developed across the resistor II'I causes the control grid tobuild up to a voltage of approximately minus 1,000 volts. With other'iield' displacements diierent voltages should befuse'df. In operatingthe resnatron tube, the two resolf nators are first tuned tosubstantially the 'same frequency by means of handwheel 43. The direct,ycurrent voltages are then applied tothe elements in the tube andoscillations are initiated, Y1building'V up gradually until the controlgrid reaches operati-, ing voltage. Then in a half-cycle when'thefield,` within the rst resonator is in a direction to aid-- movement ofthe electrons, a group of .electrons are liberated from the cathodeduring the peakI portion only of the half-cycle and move towardv theanode, picking up energy from the high-fre#` speed. WithA this greatlyincreased speed, the

electrons enter the second resonator approxilmately one-quarter. of acycle `after leaving the cathode and with the phase displacement of theorder of degreesbetween the fields of therst and second resonators, theiield of the second resonator is, at that time, in a direction opposingthe motion of the electrons. Consequently, ,the electronsgive up energyto the eld of the second reasonator producing the oscillations therein.Sufficient power is fed back from the second reso nator to the rstresonator throughv the coupling1 wires 99 to maintain the oscillationsin. the rst resonator and the greater remaining power in the secondresonator is extracted by a coupling loop and fed to an output line 91.

It is to be noted that the feed-back coupling wire provides an eiiicientfeed-back system ref. quiring but a Very low current with low losses andavoids any vacuum problems. In addition, the coupling `wire provides asuitable phase-shifting circuit to displace the phase of the field ofthe rst resonator with respect to the field ofthe second resonator andthus enables higher .direct-, current voltages to be employed resultingin a greater output power from the tube.

Although I have shown and described a specific4 embodiment of myinvention, I am aware that other suitable modifications may be made..1,

the specific embodiment disc1osed .A

I claim as my invention:

1. An electronic tube apparatus comprising a pair of hollow bodyresonators adapted to have electromagnetic eld oscillations establishedtherein, an anode mounted within one of said resonators, a cathodeymounted Within the other of said resonators, said pair of resonatorsbeing adjacent each other with openings therein be tween said anode andcathode permitting a ow of electrons from said cathode to said anode, acontrol grid between said cathode and anode, circuit means connected tosaid anode and cathode for establishing a direct current potential fieldtherebetween tending to liberate electrons from said cathode and movethem toward the anode, additional circuit means connected to said gridand cathode for establishing a direct current potential iield permittingelectrons to be liberated from the cathode during the peak portion onlyof a half-cycle oi the eld within said other` resonator in which it isof a polarity to add energy to the electrons, the strengths of saidields movingsaid liberated electrons toward said anode with a speedcausingr them to pass through said one resonator to said anode while theeld therein opposes their motion and absorbs energy therefrom, and afeed-back coupling between said resonators for supplying energy fromsaid one resonator to said other resonator to maintain the field thereinat substantially the same frequency but displaced in phase relative tothe eld of the second resonator, said coupling comprising a conductorconnected at one end to said cathode and extending into said oneresonator with the other end thereof adjacent to, but spaced from, saidanode to form a capacity connected between said anode and cathode, andtuning means connected to one of said resonators for adjusting theresonant irequency thereof whereby the amount of said phase displacementmay be adjusted.

2. An electronic tube apparatus comprising a pair of hollow bodyresonators adapted to have electro-magnetic eld oscillations establishedtherein, an anode mounted within one of said resonators, a cathodemounted Within the other of said resonators, said pair of resonatorsbeing adjacent each other with openings therein be- 10 tween said anodeand cathode permitting a flow of electrons from said cathode to saidanode, control grid between said cathode and anode, cir-- cuit meansconnected to said anode and cathode for establishing a direct currentpotential field therebetween tending to liberate electrons from saidcathode and move them toward the anode, additional circuit meansconnected to said grid and cathode for establishing a direct currentpotential eld permitting electrons to be liberated from the cathodeduring the peak portion only oi a halfcycle of the eld within said otherreso nator in which it is of a polarity to add energy to the electrons,the strengths of said ieids mov ing said liberated electrons toward saidanode with a speed causing them to pass through said one resonator tosaid anode while the field therein opposes their motion and absorbsenergy there from, and a feed-back coupling between said resonators forsupplying energy from said one resonator to said other resonator tomaintain the field therein at substantially the saine frequency butdisplaced in phase relative to the field of the second resonator, saidcoupling comprising a conductor connected at one end to said cathode ata point of substantially maximum high frequency eld voltage andextending into said one resoa nator with the other end thereof adjacentto, but spaced from, said anode to form a capacity connected betweensaid anode and cathode, and tuning means connected to one of saidresonators for adjusting the resonant frequency thereof whereby theamount of said phase displacement may be adjusted.

DAVID ii. SLOAN.

REFERENCES CITED The following references are of record in the nie o1this patent:

UNITED STATES PATENTS Number Name Date 2,088,722 Potter Aug. 3, 19372,157,952 Dallenbach May 9, 1939 2,287,845 Varian et al. June 30, 19422,389,271 Mouromtseff et al` Nov. 20, 1945

